1. Field of the Invention
The present invention relates to an image sensor. More particularly, the present invention relates to an image sensor having an inner lens formed in a color filter portion to enable incident light to reach a condensing lens, so that the incident light may further reach photodiodes. Thus, light loss can be reduced and photosensitivity can be improved.
2. Discussion of the Related Art
An image sensor is a semiconductor module that converts optical images to electrical signals. Image sensors may be charge-coupled devices (CCD) or complementary-metal-oxide-semiconductor (CMOS) image sensors. Such image sensors employ photodiodes to detect a light signal, and resolution is determined by the number of photodiodes existing in an image plane. The photodiodes receive images. Each photodiode represents a key element of one pixel unit, which includes a corresponding color filter of a color filter array and a corresponding microlens, all of which may be integrated on a single chip. With the demand for increased resolution along with greater miniaturization, more pixels are needed per unit area, which requires a decrease in pixel size. As a result, a photodiode area is reduced accordingly, thereby reducing photosensitivity.
To compensate photosensitivity, an inner lens may be additionally formed. The inner lens enables incident light to adapt to variations of a condensing angle due to an F-number. The inner lens also compensates for stray light that occurs due to the long travel distance to the photodiode area. The inner lens may be formed of an organic material or an inorganic material. If the inner lens is formed of an organic material, a positive photoresist having fluidity is used. Therefore, the process of forming the inner lens of an organic material is the same as the process of forming a condensing lens formed on a color filter portion. That is, the inner lens may be also formed by coating, exposure, development, bleaching, curing, and planarizing the color filter portion.
If a photoresist having fluidity is used, a problem in controlling critical dimension due to notching occurs. The notching occurs as the photoresist is affected by a light-shielding metal layer to be coated with the photoresist. For this reason, problems occur in that the process of forming the inner lens is complicated and an additional interlayer process is required.